Electric conductor rails

ABSTRACT

An electric conductor rail for engagement by opposed current collectors comprises two contact members of a hard-wearing material having a substantial electrical conductivity. The contact members have channel-shaped portions arranged back-toback to receive the current collectors, and an integral extension of a first of the arms of each channel-shaped portion. The integral extensions form a channel in which is received a conductor member which has a high electrical conductivity and which is forced into intimate contact with the first arms at least at intervals along the conductor rail.

451 Sept. 4, 1973 ELECTRIC CONDUCTOR RAILS [75] Inventor: George Robert Falkiner-Nuttall,

Richmond, Surrey, England [73] Assignees Tracked Hovercraft Limited,

London, England 22 Filed: Sept. 7, 1971 211 Appl.No.: 178,107

[30] Foreign Application Priority Data 2,057,273 10/1936 Little [74/129 8 1,350,856 8/1920 Davis 191/22 R FOREIGN PATENTS OR APPLICATIONS 329,717 5/1930 Great Britain 191/29 Primary Examiner-Gerald M. Forlenza Assistant Examiner- D. W. Keen Att0rneyG. W. Daisley [57] ABSTRACT An electric conductor rail for engagement by opposed current collectors comprises two contact members of a hard-wearing material having a substantial electrical conductivity. The contact members have channelshaped portions arranged back-to-back to receive the current collectors, and an integral extensionof a first of the arms of each channel-shaped portion. The integral extensions form a channel in which is received a conductor member which has a high electrical conductivity and which is forced into intimate contact with the first arms at least at intervals along the conductor rail.

18 Claims, 8 Drawing Figures Sept. 8, 1970 Great Britain 42,979/70 [52] US. Cl. 191/29, 191/32 [51] Int. Cl. B60m H30 [58] Field of Search 174/129 B, 133 B; 191/22, 23, 28, 29, 30, 32, 33, 45, 49, 48, 57, 58

[56] References Cited UNITED STATES PATENTS 465,886 12/1891 Pruyn 191/22 R 2,122,248 6/1938 Scott 174/129 B PATENTED 5 3.751059 SHEET 3 [IF 4 PATEN ED 3.757. 059

SHEEN or 4 ELECTRIC CONDUCTOR RAILS This invention relates to an electric conductor rail of the kind adapted for engagement by current collectors which engage the conductor rail in opposed relationship in the manner of a caliper.

An object of the invention is to provide such a conductor rail which is relatively cheap and reliable and which is suitable for use in current systems for vehicles operating at high speeds, for example, 250 kilometres per hour.

According to the present invention an electric conductor rail for engagement by current collectors arranged to contact the conductor rail in opposed relationship in the manner of a caliper comprises two contact members of a hard-wearing material having a substantial electrical conductivity and each having a channel-section portion formed of a generally planar contact yoke with collector guidance arms extending generally perpendicularly therefrom at either end and an integral extension of a first of the guidance arms, the contact members being secured together with their contact yokes back-to-back so that the extensions form with the first guidance arms a further channel extending along the conductor rail, at least one further member bridging the further channel and secured to the extensions, and a conductor member of high electrical conductivity extending along the further channel between the further member and the first arms and forced into current transfer relationship with the first, arms by clamping means reacting against the further member.

The further member, which may also be adapted for attachment to a structure whereby to support the rail in position, may be one of a plurality of members spaced along the conductor rail or it may be a generally continuous member. Preferably it has a generally channel-shaped cross section and is concave to the further channel.

Preferably the yokes are spaced apart by one or more spacing members. Where expansion joints are provided in the conductor rail, the discontinuities in the contact members at the expansion joints are preferably bridged by free-sliding end parts of the spacing member or members so as to provide mechanical continuity along the conductor rail in respect of bending moments whilst allowing the required expansion and contraction of the discontinuities.

These and other features of the invention will become apparent from the following description, given by way of example and with reference to the accompanying drawings, of a conductor rail in accordance with the invention. In the drawings:

FIG. I shows the conductor rail forming the embodiment of the invention in its application to a high speed ground transportation system (shown in transverse cross-section) in which a gas cushion vehicle is arranged for operation along a prepared track;

FIG. 2 shows the conductor rail in transverse crosssection, also illustrating its operation;

FIG. 3 shows in side elevation a part of the conductor rail which is different from that shown in FIG. 2;

FIG. 4 is a perspective view showing in detail one of the members included in FIG. 3;

FIG. 5 is a perspective view showing one type of expansion joint in the conductor rail;

FIG. 6 is a perspective view showing in detail one of the members included in FIG. 5; and

FIGS. 7a and 7b, when joined along the lines A-A, constitute a side elevation of a second type of expansion joint in the conductor rail.

Referring now to FIG. 1 of the drawings, a gas cushion vehicle 1 is arranged for operation along a rectangular concrete track 2 supported at intervals by supports 3. The vehicle is supported above the track by a flexibly mounted support pad 4 at each end of the vehicle, through the medium of cushions of air generated and maintained between the pads and the horizontal top surface 5 of the track. Likewise, the vehicle is guided along the track by pairs of opposed flexibly mounted guidance pads 6 at the front and rear of the vehicle co-operating, through the medium of cushions of air, with the vertical side surfaces 7 of the track. Further flexibly mounted gas cushion pads 8 are mounted below the guidance pads 6 at the rear of the vehicle for providing stiffness against vehicle rolling motions due to, for example, side winds.

Propulsive force for the vehicle is provided by a single-sided linear induction motor having its primary member 9 carried by the vehicle body for co-operation with a secondary member 10 extending along the track and inset centrally into the top track surface 5.

Electric power for the primary member 9 and also for the other electrical devices on the vehicle 1 (such as the fans supplying air to the pads 4, 6 and 8) is provided by three current collector pick-up devices 11 which contact respective conductor rails 12 extending in parallel and horizontal relationship along the track.

The pick-up devices 11 are attached to the vehicle body by respective drag arms 13 which extend downwardly and backwardly to the devices from the vehicle body. Universal joints (not shown) at the ends of each drag arm substantially prevent transverse movements of the vehicle on its track from affecting the devices 1 l.

The conductor rails are identically supported at regular intervals (e.g. two metres) along the track by insulators 14 mounted on support arms 15 which are attached to the underside of the track and each of which serves all these conductor rails. For operation the conductor rails are connected to respective phases of a three-phase trackside supply (not shown).

Referring now to FIG. 2, each conductor rail is basically formed of opposed contact members 20 which are either pressed or rolled from sheet or extruded to the required shape, and a conductor 21 made of a material having a high electrical conductivity such as aluminum or aluminium alloy.

The members 20, which are made of a hard-wearing but reasonably electrically conductive material such as copper-bearing steel, are each generally in the form of a U which is turned on its side and has its upper and lower arms 22, 23 perpendicular to its yoke 26. The members 20 are arranged in back-to-back configuration with their yokes 26 separated by a generally continuous sheet steel spacing member 27. Welds 28, 29 (which may be continuous) are made along the upper and lower edges of the spacing member 27 so as to secure the members 20, 27 together as a rigid structure. In a modification the generally continuous member 27 is replaced by a plurality of separate members of the same cross-section and at a suitable longitudinal spacing.

The arms 23 of the members 20 are integrally formed at their ends with downwardly turned vertical extensions 24 which, together with the arms 23, form an open-bottomed channel 25 along the bottom of the conductor rail. In this channel is centrally received the conductor 21.

As illustrated in FIG. 2, the conductor 21 is pressed firmly in position against the underside of the arms 23 by bolts 30 threaded in short channel members 31.

These channel memebers are upwardly facing (and therefore concave to the channel 25) and are provided along the conductor rail at intervals. They nestle between the extensions 24 and are secured to the extensions by bolts 32 threaded into their arms 33. At their free ends the arms 33 are interposed between the edges of the conductor 21 and the extensions 24 so as to locate the conductor laterally in position. Although as so far described the conductor rail is continuous, the constituent members 20, 21 are, in fact, formed in lengths secured together end-to-end. The joints between adjacent lengths of the contact members 2 occur at every second support arm 15. The arrangement of one such joint will be apparent from FIGS. 3 and 4 from which it will be seen that the joint 91 is bridged by an upwardly facing channel member 36 shown in detail in FIG. 4. The member 36 is centrally formed with a hole 37 through which passes a bolt 38 threaded into the underlying insulator 14, and two further holes 39 in which are threaded further bolts having the same function as the bolts 30 of FIG. 2 and therefore given the same reference numeral. The channel member 36 has upstanding arms 40 formed with threaded holes 92; these holes are engaged by further bolts 41 to secure the member 36 to the extensions 24 on either side of the joint 91.

The channel members 36 therefore serve not only to attach the conductor rails to insulators 14, but also to bridge the joints in the contact members 20 and to provide lateral location for the conductor 21 in the manner of the channel members 31. They also clamp the conductor firmly against the arms 23; the forces exerted on the arms 23 by the bolts 30 deform them resiliently to some extent, and their resilience helps to maintain the desired upward pressure on the conductor despite vibration etc. of the conductor rail.

The separate lengths of the conductor 21 are arranged to overlap one another at their ends and are bolted together where they overlap. The connections so formed are offset from the joints between the lengths of each contact member 20, and are not shown in the drawings; to enable them to be readily accessible in the assembled conductor rail, the lengths of conductor 21 on either side of each connection are cranked downwardly so that the connection lies below the bottom of the extensions 24.

Further channel members (not shown) similar to the channel members 36 likewise connect the midpoint at each length of contact member 20 to the underlying insulator 14 as well as resiliently reacting clamping forces produced on the conductor 21 by further bolts 30 and locating the conductor laterally in position.

In addition to the joints between the lengths of its constituent members 20, 21, at occasional intervals (e.g., 50 metres) along its length each conductor rail is formed with an expansion joint for accommodating differential thermal expansion and contraction between itself and the track. A typical expansion joint is shown in FIG. from which it will be seen that in the members 20 the expansion gap is in the form of a parallel-sided discontinuity 42. In the arms 22 the discontinuity is angled in opposite senses at 30 from the central vertical plane along the conductor rail, so that as seen from above it has the form of a chevron. From this chevron the discontinuity 42 extends in the yokes 26 at an angle of 60 to a transverse plane through the conductor rail, to a further chevron formed in the arms 23 and thence vertically downwards in the extensions 24.

The spacing member 27 is also discontinuous at the expansion joint, being formed with a gap 43 at one side of the discontinuity 42 in the yokes 26. The spacing member, which therefore bridges the discontinuity 42, has its part between the gap 43 and the discontinuity 42 free to slide between the yokes 26 at its sides. The gap 43 is sufficient to accommodate the maximum expansion of the conductor rail relative to its track so that at the expansion joint there is provided a means for maintaining transverse alignment of the conductor rail on the two sides of the expansion joint at all times whilst accommodating expansion and contraction of the expansion joint due to differential thermal changes between conductor rail and track.

The conductor 21 at the expansion joint is discontinuous but is electrically bridged by two short prefabricated jumpers arranged side-by-side one beneath each arm 23 and each having a flexible central portion; each jumper is bolted at its ends to the ends of the conductor 21 proper at their undersides.

FIG. 5 also shows that the conductor rail has support provided on each side of the expansion joint by a common support arm 15 via individual insulators 14. The insulators are each attached to the conductor rail by a respective upwardly facing channel member 44 (FIG. 6) bolted to the insulator by a bolt (not shown) extending through a hole 45.

On one side of the expansion joint (the right-hand side as shown) the extensions 24 of the conductor rail are bolted tightly by bolts 47 engaging the arms 46 of the respective channel member 44 at threaded holes 93. The extensions 24 on the other side of the expansion joint, however, are formed with longitudinal slots 48, and through these slots extend studs 49 screwed into the arms 46 of the other channel member 44. In operation any relative movement of the ends of the conductor rail at the expansion joint (with consequent expansion or contraction of the discontinuity 42) will be accommodated by movement of the slots 48 relative to the studs 49. It will be noted in this respect that apart from the movement of the studs 49 along the slots 48 at each expansion joint relative movement between conductor rail and track is otherwise accommodated by flexing of the support arms 15.

In a modification, for each length of conductor rail between expansion joints the bolts 41 and 47 are replaced by studs like the studs 49 and their associated holes are slotted (like the slots 48), except at one point along the length. Each length of conductor rail between expansion joints will then expand and contract away from its fixed point without flexing of the support arms 15. The fixed pivot may conveniently be midway along the length, or it may be at one end as is shown at the right of the discontinuity 42 in FIG. 5.

The expansion joint of FIG. 5 is suitable for accommodating a movement of up to, say, five centimetres but is unsuitable where any greater movement is possible such as at the expansion gap 94 (FIG. 7a) between long lengths (e.g., 300 metres) of continuous track. FIGS. 7a and 7b show a multiple expansion joint which can accommodate movements of the order of four times the movement which can be accommodated by the arrangement of FIGS. 5 and 6.

The multiple expansion joint is provided between end portions of the conductor rail which are individually secured to the track by insulators 14 and channel members 44 (not visible), as previously described in relation to FIGS. 5 and 6 for the conductor rail to the right of the discontinuity 42. In FIGS. 7a and 7b these two end portions are indicated generally by the reference numerals 50 and 51.

Four regularly spaced discontinuities 52, 53, 54 and 55 are provided in series between the end portions 50 and 51 so as to subdivide the conductor rail into three short sections 56, 57 and 58. So far as the contact members 20 are concerned, each discontinuity is identical to the discontinuity 42 described with reference to FIG. 5 being likewise bridged by the spacing member 27.

The support arms on which the end portions 50 and 51 are mounted via their respective insulators 14 are each formed with three holes, one beneath each insulator. For each conductor rail holes in the two support arms 15 are aligned and receive in sliding relationship a support beam 59 bridging the gap between them. The support beam in' turn carries six insulators 60 which are similar to the insulators l4 and are regularly spaced between the support arms 15 carrying the beam.

At each end of the beam 59 the last two insulators 60 are individually attached to the respective portion 56 or 58 of conductor rail in the manner described with reference to FIGS. 5 and 6 in relation to the insulator 14 at the left'hand side of the discontinuity 42. Thus the conductor portions 56, 58 are free to move to a predetermined limited extent longitudinally relative to the support beam 59.

The portion 57 of the conductor rail is firmly fixed to the underlying insulators 60 in the manner described in relation to the conductor rail at the right-hand side of the discontinuity 42 in FIGS. 5 and 6.

Electrical continuity for the conductor 21 across the multiple expansion joint is provided by jumpers 80 similar to that previously described in relation to FIGS. 5 and 6 and connected in pairs across each discontinuity 52 to 55 between aluminum channel members 61, 62 and 63 which are bolted by bolts 64 to the extensions 24 of the respective sections 56, 57 and 58.

Slotted links 65 mounted on, and engaged by, pins 66, 67 respectively individually bridge the discontinuities 52 and 55 at the extensions 24 on either side of the conductor rail so as, with the pin and slot mechanisms comprising the items 48, 49 to limit each discontinuity to a maximum width of one quarter of the total estimated extension of the expansion gap as a whole. Generally speaking, the discontinuities expand or contract successively (rather than simultaneously), each discontinuity opening or closing to its maximum extent before the next discontinuity is affected.

In a modification of the arrangement of FIGS. 70 and 7b, the links 65 are rigidly attached to the extensions 24 of the short sections 56 and 58 instead of being pivotally mounted on the pins 66. The slot and pin mechanisms (comprising the links 65 and pins 67) then provide support for the sections 56 and 58 in addition to that provided by the insulators 60.

Instead of an expansion joint of the kind shown in FIGS. 7a and 7b having three (or more) short sections immediately adjacent one another, it may be desirable to accommodate a large movement by means of two or more expansion joints each having two discontinuities forming one short section of conductor rail and spaced apart along the rail. Conveniently the adjacent ends of the larger rail sections at either side of these short rail sections are individually supported by a common support arm as shown in FIG. 5 and in a manner to allow for the required movement. The short sections may each be wholly supported in position by slotted, rigidly mounted links and co-operating pins as in the previous paragraph, the slots provided in the links each having a length which is half the required movement.

In a non-illustrated modification of the arrangements of FIGS. 5 to 7b, at each discontinuity the free end of the spacing member 27 is located vertically along its top and bottom edges by two horizontal plates one of which extends across the top of the rail adjacent to, and welded to, the arms 22, and the other of which is likewise welded to the underside of the arms 23 within the channel 25.

Referring again to FIG. 2, each conductor rail in operation has its yokes 26 engaged by a longitudinally spaced pair of opposed carbon shoes each subdivided into two vertically spaced pairs. For clarity only one shoe is indicated (in general outline) in FIG. 2; it is denoted by the reference numeral 69. The opposed shoe is identical to this shoe and is arranged as a mirror image thereto.

The shoes are mounted in caliper fashion on respective arms of a bifurcated yoke attached to the respective drag arm 13 (FIG. 1), and are biassed towards one another so as to engage the plane outer surfaces of the yokes 26 in good current transfer relationship. Guidance for each current collector pick-up device 11 (comprising the shoes 69 and the yoke 90) and its drag arm 13 is provided by the shoes 69 themselves. The two parts of each shoe are movable vertically relative to one another and are biassed apart by compression springs (not shown) so that the shoe as a whole expands into contact with both the upper and lower surfaces of the arms 22, 23 which then act current collector guidance arms, despite the upward force exerted on the shoe by the vehicle due to the upward inclination of the drag arm.

It will be noted that the mechanical requirements of the conductor rail to withstand the wear caused by the rubbing contact with the shoes 69 are met by the hardwearing material forming the contact members 20, whereas the requirement of high electrical conductivity is met to a large extent by the conductor 21. Electrical contact between the conductor 21 and the contact members 20 occurs where they are clamped together by the bolts 30. Between these points the conductor 21 is preferably allowed to sag so as to accommodate differential thermal expansion and contraction of the conductor and the contact members.

The invention is in no way limited to the particular orientation of the conductor rail forming the described embodiment; a conductor rail in accordance with the invention could, for example, be supported from above with the conductor above the contact members. Preferably the yokes 26 are vertical.

In a modification of the described embodiment the various channel members (e.g., 31, 36 and 44) spaced along the conductor rail are replaced by a generally continuous member which may, for example, be of rectangular cross-section. The channel in which the conductor 21 is disposed is then generally closed along its length, whereas in the described embodiment it is closed only at intervals.

Although the conductor rail of the described embodiment is attached to a generally continuous structure (i.e., the associated track) by means of spaced support arms, a conductor rail in accordance with the invention when mounted for operation may be disposed directly adjacent a generally continuous structure by which is supported, or it may be supported from the ground by spaced support columns.

I claim:

ll. An electric conductor rail, for engagement by current collectors arranged to contact the conductor rail in opposed relationship in the manner of a caliper, comprising two contact members of a hard-wearing material having a substantial electrical conductivity and each having a channel-section portion formed of a generally planar contact yoke with collector guidance arms extending generally perpendicularly therefrom at either end and an integral generally perpendicular extension to a first of the guidance arms, the contact members being secured together with their contact yokes back-to-back so that the extensions form with the first guidance arms a further channel extending along the conductor rail, at least one further member bridging the further channel and attached to the extensions, and a conductor member of high electrical conductivity extending along the further channel between the further member and the first arms and forced into current transfer relationship with the first arms by clamping means reacting against the further member.

2. A conductor rail according to claim 1 wherein the further member is of a generally channel-shaped crosssection, having arms attached to the extensions and being concave to the said further channel.

3. A conductor rail according to claim 2 wherein the arms of the further member are interposed between the conductor member and the extensions so as to provide lateral location for the conductor member.

4. A conductor rail according to claim 1, wherein the further member is adapted for attachment to a structure whereby to support the rail in position for operation.

5. A conductor rail according to claim It, comprising a plurality of the said further members spaced along the conductor rail.

6. A conductor rail according to claim 1, wherein along their lengths the yokes are spaced apart by at least one spacing member interposed therebetween.

7. A conductor rail according to claim 6, which includes a plurality of the said spacing members spaced apart along the conductor rail.

8. A conductor rail according to claim 6, wherein the contact members are secured to one another and to the or each spacing member by welding along the edges of the or each spacing member.

9. A conductor rail according to claim 1, which includes an expansion joint comprising a discontinuity in the contact members, in each contact member the discontinuity being inclined to a transverse plane relative to the conductor rail both at the yokes and at the arms of the channel-section portion, the conductor rail comprising a plate member which extends from between the yokes on one side of the discontinuity to between the yokes on the other side so as to bridge the discontinuity, the plate member being slidable relative to the conductor rail on one side of the discontinuity so as to allow the discontinuity to expand and contract whilst maintaining transverse alignment of the conductor rail on the two sides of the expansion joint in the direction perpendicular to the yokes.

10. A conductor rail according to claim 9, wherein in the first arms of the channel-section portions the discontinuity is oppositely inclined longitudinally of the conductor rail so as to be in the form of a chevron, the discontinuity forming a further chevron in the other said arms of the channel-section portions.

11. A conductor rail according to claim 1, which includes a support member adapted for attachment to a structure whereby to support the conductor rail in position, the support member bridging the further channel and attached to each extension by means of a pin and slot mechanism allowing a predetermined longitudinal movement of the conductor rail relative to the structure.

12. A conductor rail according to claim 11, which includes an expansion joint comprising a discontinuity in the contact members, the said support member being adapted to support the conductor rail at one side of the discontinuity, the conductor rail comprising a further support member bridging the further channel at the other side of the discontinuity and secured to the extensions, the further support member being adapted for attachment to a structure whereby to support the conductor rail at the other side of the discontinuity.

13. A conductor rail according to claim 12, whereinthe support member and the further support member are connected rigidly to a common said structure.

14. A conductor rail according to claim 1, which includes an expansion joint comprising a discontinuity in the contact members, the conductor rail including a respective link carried by each extension on one side of the discontinuity and formed with a slot engaged by a pin carried by the same extension on the other side of the discontinuity for limiting the width of the discontinuity to a predetermined value.

15. A conductor rail according to claim 14, wherein each link is rigid with the extension which carries it so as in combination with the co-operating pin to maintain transverse alignment of the conductor rail on the two sides of the expansion joint in the direction parallel to the yokes.

16. A conductor rail according to claim 15, wherein each link is pivotally carried on the respective extension.

17. An electric conductor rail, for engagement by current collectors arranged to contact and slide along oppositely facing surfaces of the conductor rail in the manner of a caliper, said rail comprising two contact members of a material having relatively high resistance to mechanical wear and having a substantial electric conductivity, each of said contact members having a channel-section portion formed of a generally planar contact yoke having guidance flanges extending generally perpendicular therefrom at either end, said contact members being secured together with their contact yokes back-to-back to provide two outwardly facing guidance channels for said current collectors and a member of high electrical conductivity extending along the rail and mounted in current transfer relation with the outer surfaces of two adjacent guidance flanges of said contact members so as to form a high conductivity bridge between said contact members, and a high conlocated in a channel formed between integral generally ductivity path lengthwise of said rail. perpendicular extensions to the adjacent guidance 18. An electric conductor rail as claimed in claim 17, flanges of said contact members. wherein the member of high electrical conductivity is 

1. An electric conductor rail, for engagement by current collectors arranged to contact the conductor rail in opposed relationship in the manner of a caliper, comprising two contact members of a hard-wearing material having a substantial electrical conductivity and each having a channel-section portion formed of a generally planar contact yoke with collector guidance arms extending generally perpendicularly therefrom at either end and an integral generally perpendicular extension to a first of the guidance arms, the contact members being secured together with their contact yokes back-to-back so that the extensions form with the first guidance arms a further channel extending along the conductor rail, at least one further member bridging the further channel and attached to the extensions, and a conductor member of high electrical conductivity extending along the further channel between the further member and the first arms and forced into current transfer relationship with the first arms by clamping means reacting against the further member.
 2. A conductor rail according to claim 1 wherein the further member is of a generally channel-shaped cross-section, having arms attached to the extensions and being concave to the said further channel.
 3. A conductor rail according to claim 2 wherein the arms of the further member are interposed between the conductor member and the extensions so as to provide lateral location for the conductOr member.
 4. A conductor rail according to claim 1, wherein the further member is adapted for attachment to a structure whereby to support the rail in position for operation.
 5. A conductor rail according to claim 1, comprising a plurality of the said further members spaced along the conductor rail.
 6. A conductor rail according to claim 1, wherein along their lengths the yokes are spaced apart by at least one spacing member interposed therebetween.
 7. A conductor rail according to claim 6, which includes a plurality of the said spacing members spaced apart along the conductor rail.
 8. A conductor rail according to claim 6, wherein the contact members are secured to one another and to the or each spacing member by welding along the edges of the or each spacing member.
 9. A conductor rail according to claim 1, which includes an expansion joint comprising a discontinuity in the contact members, in each contact member the discontinuity being inclined to a transverse plane relative to the conductor rail both at the yokes and at the arms of the channel-section portion, the conductor rail comprising a plate member which extends from between the yokes on one side of the discontinuity to between the yokes on the other side so as to bridge the discontinuity, the plate member being slidable relative to the conductor rail on one side of the discontinuity so as to allow the discontinuity to expand and contract whilst maintaining transverse alignment of the conductor rail on the two sides of the expansion joint in the direction perpendicular to the yokes.
 10. A conductor rail according to claim 9, wherein in the first arms of the channel-section portions the discontinuity is oppositely inclined longitudinally of the conductor rail so as to be in the form of a chevron, the discontinuity forming a further chevron in the other said arms of the channel-section portions.
 11. A conductor rail according to claim 1, which includes a support member adapted for attachment to a structure whereby to support the conductor rail in position, the support member bridging the further channel and attached to each extension by means of a pin and slot mechanism allowing a predetermined longitudinal movement of the conductor rail relative to the structure.
 12. A conductor rail according to claim 11, which includes an expansion joint comprising a discontinuity in the contact members, the said support member being adapted to support the conductor rail at one side of the discontinuity, the conductor rail comprising a further support member bridging the further channel at the other side of the discontinuity and secured to the extensions, the further support member being adapted for attachment to a structure whereby to support the conductor rail at the other side of the discontinuity.
 13. A conductor rail according to claim 12, wherein the support member and the further support member are connected rigidly to a common said structure.
 14. A conductor rail according to claim 1, which includes an expansion joint comprising a discontinuity in the contact members, the conductor rail including a respective link carried by each extension on one side of the discontinuity and formed with a slot engaged by a pin carried by the same extension on the other side of the discontinuity for limiting the width of the discontinuity to a predetermined value.
 15. A conductor rail according to claim 14, wherein each link is rigid with the extension which carries it so as in combination with the co-operating pin to maintain transverse alignment of the conductor rail on the two sides of the expansion joint in the direction parallel to the yokes.
 16. A conductor rail according to claim 15, wherein each link is pivotally carried on the respective extension.
 17. An electric conductor rail, for engagement by current collectors arranged to contact and slide along oppositely facing surfaces of the conductor rail in the manner of a caliper, said rail comprising two contact members of a material Having relatively high resistance to mechanical wear and having a substantial electric conductivity, each of said contact members having a channel-section portion formed of a generally planar contact yoke having guidance flanges extending generally perpendicular therefrom at either end, said contact members being secured together with their contact yokes back-to-back to provide two outwardly facing guidance channels for said current collectors and a member of high electrical conductivity extending along the rail and mounted in current transfer relation with the outer surfaces of two adjacent guidance flanges of said contact members so as to form a high conductivity bridge between said contact members, and a high conductivity path lengthwise of said rail.
 18. An electric conductor rail as claimed in claim 17, wherein the member of high electrical conductivity is located in a channel formed between integral generally perpendicular extensions to the adjacent guidance flanges of said contact members. 